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Techniques for Dosing and Blending Masterbatch
There are a number of possibilities that can be used with masterbatch to produce a product that incorporates the properties of the masterbatch homogeneously. In this article we’ll survey the main methods, from the use of compound, through batch blenders, to masterbatch dosers. We’ll examine the main advantages and disadvantages of each method.
Compound is a customized, premixed raw material. During its production process masterbatch is used, so the properties of the masterbatch are extremely homogeneous in a product made of compound. In order to use compound, the manufacturers must order specific compound for each product and type of masterbatch.
Illustration 1: Compound
Due to the compound’s homogeneity, one can produce products of uniform and consistent quality and it’s also simple and easy to use, with no need for additional dosing equipment for the masterbatch. That being said, the cost of the compound is higher than the cost of separate virgin raw material and masterbatch with online dosing. Also, a large quantity and variety must be kept in stock and as a result, operational costs are high. The use of compound limits flexibility in switching recipes and thorough cleaning is required between compounds.
One can differentiate between two types of batch blenders – a central batch blender and a local batch blender. In central batch blending, the dosing and mixing are carried out at a central location by one or more central batch blenders, assigned to one machine or a number of machines using an identical recipe. In local batch blending, the dosing and blending are carried out for each manufacturing machine separately, on or adjacent to the machine.
Illustration 2: Batch blender
Central Batch Blender
The number and size of central batch blenders depends on the number of machines, the number of materials, and the recipes. The use of central batch blenders saves space on the production floor and also requires less equipment. In addition, with central batch blenders one can easily carry out centralized control, and operation and maintenance are also simpler.
However, a lot of equipment and floor space is needed when working simultaneously with many kinds of masterbatch and flexibility is low when you want to switch the masterbatch or the recipe. In addition, due to the long-distance transport, there’s a separation of ingredients and a diversity of material properties and when there’s a change of recipe the reaction time is slow, resulting in a waste of raw materials. Another limitation of central batch blenders is that it isn’t possible to gather specific data regarding each machine or job.
Local Batch Blender
In contrast to the central batch blender, the local batch blender gives better precision, since it’s located on or adjacent to the manufacturing machine.
It also allows high flexibility when switching recipes, its reaction time is faster, and it saves space on the production floor (if installed on the neck of the machine).
On the other hand, with the use of local batch blenders the feeding of materials is more complicated since it requires a separate raw material tube for each machine and a large number of loaders, the maintenance is tedious (when it’s installed above the machine), and there’s more manual intervention when switching raw materials. There also isn’t always room above or next to the machines.
A Separate Masterbatch Feeder on the Machine's Throat
The use of a masterbatch feeder on the machine's throat allows flexibility when working with a number of masterbatches. The cleaning process is easy, the setup is simple, and it saves floor space.
There are two types of masterbatch feeders – volumetric and gravimetric. The volumetric feeder works at a constant auger speed and is relatively inexpensive, while the cost of a gravimetric feeder is a bit higher and it works with online control of each dose and ongoing adjustment.
Illustration 3: Masterbatch feeder
Volumetric Masterbatch Feeder
The volumetric masterbatch feeder is a simple feeder and, as mentioned, relatively inexpensive. It’s actually the least expensive solution of all for masterbatch dosing. However, its price is its only advantage while it has many drawbacks.
The biggest disadvantage is that the use of a volumetric masterbatch feeder ultimately results in a high consumption of masterbatch, so the savings on the cost of the instrument is equaled or even exceeded by the extra costs of using it, such as the surplus amount of masterbatch and other costs.
The volumetric feeder works with a constant auger speed, however the parameters of the masterbatch, such as its bulk density, may vary from batch to batch and even within the same batch. Since the auger speed of the feeder remains constant, the result is deviation in the doses delivered by the volumetric feeder. Deficient doses result in rejected products and the consequent costs. One can avoid rejected products by setting the volumetric feeder to dispense a larger dose, but the result is the cost of overconsumption of masterbatch.
Volumetric feeders usually require lengthy calibration and setup processes and a skilled crew is required to carry out these processes with every change in recipe or masterbatch, leading to a relatively long interruption of production. In addition, with many volumetric feeders the auger speed doesn’t change with a change in the parameters of the manufacturing process, such as the dosing time, leading to even worse performance. Also, when using volumetric feeders it’s not possible to gather true cumulative data regarding amounts, but only theoretical data.
Gravimetric Masterbatch Feeder
The gravimetric masterbatch feeder works by the loss-in-weight method, and each dose is controlled online, with adjustments being made for every deviation in the parameters of the process or the raw materials. In this way you get high levels of accuracy, repeatability, and homogeneity. This leads to significantly lower consumption of masterbatch (see illustration 4), up to 50% less than the volumetric feeder, and therefore in the long run the use of a gravimetric feeder is more economical than the use of a volumetric feeder despite the slightly higher cost of the gravimetric feeder.
Illustration 4: Comparison of gravimetric and volumetric feeders
In addition to the significant savings as a result of the use of a low percentage of masterbatch, the use of a gravimetric feeder allows the use of masterbatch with a high percentage of pigment as a result of the high accuracy, lowering the cost of the masterbatch even more.
With a gravimetric feeder calibration is simple, recalibration isn’t necessary when changing materials or recipes, and setup time is minimal. Also, with a gravimetric feeder cumulative data can very easily be gathered in real time.
After examining all the methods of masterbatch dosing and blending, we can see that the use of a gravimetric masterbatch feeder is better than all the other methods both cost-wise and operation-wise.
In comparison with compound, the use of a gravimetric masterbatch feeder saves on raw material costs and stock and operational costs, and allows high flexibility when changing recipes.
Compared to the volumetric feeder, the gravimetric feeder is preferable in all respects and even though its price is slightly higher, the price difference is negligible compared to the long term savings that the gravimetric feeder offers.
In comparison with the batch blender, as well, the gravimetric feeder is preferable since it allows quick, easy, and thorough cleaning when changing masterbatch, it’s simple to operate, and saves production floor space. As far as performance goes, it delivers better homogeneity, making it possible to save up to 10% of the masterbatch compared to a local batch blender, and up to 20% compared to a distant batch blender.
In conclusion, among all the options we surveyed, the gravimetric feeder is the most efficient solution, giving the most accurate results, and it’s the most economical solution in the long run.